Method and Apparatus for Mobility Agent Recovery

ABSTRACT

Techniques for recovering Mobile Internet Protocol (IP) session(s) of a mobility agent in a Mobile IP network are described herein. In one embodiment of the invention, for each mobility session associated with a mobility agent, the mobility agent distributively backs up mobility agent specific information to the mobility agent peer associated with that mobility session. The mobility agent specific information is not used by the mobility agent peer. Upon the mobility agent inadvertently losing at least one mobility session, the mobility agent recovers the stored mobility agent specific information associated with those sessions from the mobility agent peers respectively associated with those sessions. Other methods and apparatuses are also described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 12/055,311,filed Mar. 26, 2008, which is hereby incorporated by reference.

BACKGROUND

1. Field

Embodiments of the invention relate to the field of Mobile IP; and morespecifically, to recovering mobility agent information.

2. Background

Mobile IP is a protocol described in Request for Comments 3344, August2002, which allows laptop computers or other mobile computing units(referred to as mobile nodes herein) to roam between varioussub-networks at various locations, while maintaining Internet and/or WANconnectivity. Mobility agents (e.g., home agent, foreign agent) provideMobile IP functionality. In a typical Mobile IP network, each mobilenode is identified by its home address (assigned by a home agent),regardless of its current point of attachment to the Internet. Whilesituated away from its home, a mobile node is also associated with acare-of address (provided by a foreign agent), which indicates itscurrent point of attachment for reachability. While a mobile node isaway from its home and connected to a foreign network it requestsregistration through the foreign agent to the home agent. If theregistration is successful, when the mobile node's home network receivespackets addressed to the mobile node, the home agent will send thosepackets, over a tunnel, to the foreign agent which in turns forwards thepackets to the mobile node. When the mobile node is sending packets, theforeign agent may employ reverse-tunneling and send the packets to thehome agent who in turn forwards the packets to their destination, or theforeign agent may directly forward the packets to their destinations.When the mobile node is successfully registered, the mobile node hasstarted a Mobile IP session. When the mobile node is deregistered (e.g.,the bindings for the mobile node have been removed), the Mobile IPsession has ended. Typically, if a mobility agent restarts, the mobilitybindings stored in the mobility agent is lost.

The Mobile IP protocol describes communicating control messages betweenthe mobility agents. For example during registration of a mobile node, aMobile IP registration request message and a Mobile IP registrationreply message are typically transmitted between a foreign agent and ahome agent. At any given time a mobility agent (either a foreign agentor the home agent) may stop providing service to the mobile node. Themobility agent that wishes to stop providing service may send aregistration revocation message, described in Request for Comments 3543,August 2003, to the peered mobility agent (e.g., a foreign agent maysend a registration revocation message to the home agent). Therevocation message informs the receiving mobility agent that the sendingmobility agent is stopping service to the mobile node. The mobilityagent that receives the registration revocation message associated witha mobile node may remove the mobility bindings for that mobile node.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may best be understood by referring to the followingdescription and accompanying drawings that are used to illustrateembodiments of the invention. In the drawings:

FIG. 1 illustrates an exemplary Mobile IP network supporting Mobile IPsession recovery according to one embodiment of the invention;

FIG. 2 is a data flow diagram illustrating Mobile IP session recovery ofa foreign agent according to one embodiment of the invention;

FIG. 3 is a data flow diagram illustrating Mobile IP session recoverywhere a mobile node is moving from one foreign agent to another foreignagent according to one embodiment of the invention;

FIG. 4 is a data flow diagram illustrating Mobile IP session recovery ina Mobile IP network with backup agents and/or recovery partnersaccording to one embodiment of the invention;

FIG. 5 is a data flow diagram illustrating Mobile IP session recoverywhere a Mobile IP conflict is detected at a mobility agent according toone embodiment of the invention;

FIG. 6 is a data flow diagram illustrating verifying Mobile IPsession(s) according to one embodiment of the invention;

FIG. 7 is a data flow diagram illustrating a hello protocol capabilityin a Mobile IP network according to one embodiment of the invention; and

FIG. 8 illustrates an exemplary mobility agent configured to supportMobile IP session recovery according to one embodiment of the invention.

FIG. 9 illustrates dynamic distribution of recovery data for mobilityagents in a Mobile IP network according to one embodiment of theinvention.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth.However, it is understood that embodiments of the invention may bepracticed without these specific details. In other instances, well-knowncircuits, structures and techniques have not been shown in detail inorder not to obscure the understanding of this description. Those ofordinary skill in the art, with the included descriptions, will be ableto implement appropriate functionality without undue experimentation.

References in the specification to “one embodiment”, “an embodiment”,“an example embodiment”, etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to effect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

In the following description and claims, the terms “coupled” and“connected,” along with their derivatives, may be used. It should beunderstood that these terms are not intended as synonyms for each other.Rather, in particular embodiments, “connected” may be used to indicatethat two or more elements are in direct physical or electrical contactwith each other. “Coupled” may mean that two or more elements are indirect physical or electrical contact. However, “coupled” may also meanthat two or more elements are not in direct contact with each other, butyet still co-operate or interact with each other.

The techniques shown in the figures can be implemented using code anddata stored and executed on one or more electronic devices (e.g., acomputer, a network element, etc.). As used herein, a network element(e.g., a router, switch, bridge, etc.) is a piece of networkingequipment, including hardware and software that communicativelyinterconnects other equipment on the network (e.g., other networkelements, computer end stations, etc.) Such electronic devices store andcommunicate (internally and with other electronic devices over anetwork) code and data using machine-readable media, such as machinestorage media (e.g., magnetic disks; optical disks; random accessmemory; read only memory; flash memory devices) and machinecommunication media (e.g., electrical, optical, acoustical or other formof propagated signals—such as carrier waves, infrared signals, digitalsignals, etc.). In addition, such electronic devices typically include aset of one or more processors coupled to one or more other components,such as a storage device, one or more user input/output devices (e.g., akeyboard and/or a display), and a network connection. The coupling ofthe set of processors and other components is typically through one ormore busses and bridges (also termed as bus controllers). The storagedevice and signals carrying the network traffic respectively representone or more machine storage media and machine communication media. Thus,the storage device of a given electronic device typically stores codeand/or data for execution on the set of one or more processors of thatelectronic device. Of course, one or more parts of an embodiment of theinvention may be implemented using different combinations of software,firmware, and/or hardware.

Techniques for recovering Mobile Internet Protocol (IP) session(s) of amobility agent in a Mobile IP network is described. In one embodiment ofthe invention, for each mobility session associated with a mobilityagent, the mobility agent distributively backs up mobility agentspecific information to the mobility agent peer associated with thatmobility session. The mobility agent specific information is not used bythe mobility agent peer. Upon the mobility agent inadvertently losing atleast one mobility session, the mobility agent recovers the storedmobility agent specific information associated with those sessions fromthe mobility agent peers respectively associated with those sessions.

FIG. 1 illustrates an exemplary Mobile IP network with mobility agentsthat support Mobile IP session recovery (hereinafter “recovery”). InFIG. 1, a mobile node 110 is coupled with a foreign agent 120 over aMobile IP connection 115. Thus, a Mobile IP session for the mobile node110 exists at the foreign agent 120 (e.g., a foreign agent type mobilitysession) and the foreign agent 120 stores Mobile IP informationassociated with the mobile node 110 specific to that foreign agent.According to one embodiment of the invention, the mobile node isanchored at the home agent 140. Thus, a Mobile IP session for the mobilenode 110 exists at the home agent 140 (e.g., a home agent type mobilitysession) and the home agent 140 stores Mobile IP information associatedwith the mobile node 110 specific to that home agent. The foreign agent120 is coupled with the home agent 140. Mobile IP data traffic 135 iscarried on a communication link between the foreign agent 120 and thehome agent 140. For example, the Mobile IP data traffic 135 is carriedon a tunnel coupling the foreign agent 120 and the home agent 140.According to one embodiment of the invention, the foreign agent 120 andthe home agent 140 are capable of recovering their mobility agent statesas designated by the foreign agent, home agent recovery 138 as describedlater herein.

The foreign agent 120 is also coupled with the foreign agent 130.According to one embodiment of the invention the foreign agent 130 is abackup foreign agent for the foreign agent 120. According to anotherembodiment of the invention the foreign agent 130 is a recovery partnerof the foreign agent 120, which is described later herein. The foreignagent 120 and the foreign agent 130 are capable of recovering theirmobility agent states as designated by the foreign agent, foreign agentrecovery 125 as described later herein.

The home agent 140 is also coupled with the home agent 150. According toone embodiment of the invention the home agent 150 is a backup homeagent for the home agent 140. According to another embodiment of theinvention the home agent 150 is a recovery partner of the home agent140, which is described later herein. The home agent 140 and the homeagent 150 are capable of recovering their mobility agent states asdesignated by the home agent, home agent recovery 145 as described laterherein. Additionally, according to one embodiment of the invention thehome agent 140 and the foreign agent 130 are capable of recovering theirmobility agent states as designated by the foreign agent, home agentrecovery 165.

The foreign agent 130 is also coupled with the home agent 150. Accordingto one embodiment of the invention the foreign agent 130 is a peer ofthe home agent 150. For example, the foreign agent 130 is providingforeign agent functionality for the home agent 150. The foreign agent130 and the home agent 150 are capable of recovering their mobilityagent states as designated by the foreign agent, home agent recovery155.

According to one embodiment of the invention, to recover their mobilityagent states (e.g., Mobile IP session information, additionalinformation pertaining to the mobile nodes (e.g., QoS parameters,traffic filters, security parameters, access control lists, loadbalancing attributes, etc.)), the mobility agents exchange recoverymessages. The recovery messages are in a request/response format withsupport for reliability. For example, in one embodiment of the inventiononly established sessions may be recovered. Reliability is achievedusing sequence numbers and acknowledgement of the sequence numbers fromthe mobility agent peer. According to one embodiment of the invention arecovery message has a UDP header followed by the following format:

The Type field indicates that this is a recovery message. For example,the bits in the Type field may indicate RECOVERY. The Subtype fielddescribes the type of recovery subtype that is carried in the message.For example, the subtype field may indicate that a Hello message, acapability negotiation (which may be a capability negotiation request orcapability negotiation reply), a bulk session recovery request, a singlesession recovery request, a bulk session recovery response, or a singlesession recovery response is carried in the particular message. Notethat it should be understood that the subtype field may be used tocommunicate different, less, or additional subtypes depending ondiffering functionalities or applications (e.g., QoS parameters,security parameters, load balancing attributes, etc.).

The MD field defines the message direction of the recovery message. Forexample, according to one embodiment of the invention if the MD fieldhas a value of 0, the message was sent from a home agent to a foreignagent. If the MD field has a value of 1, the message was sent from aforeign agent to a home agent. If the MD field has a value of 2, themessage was sent from one home agent to another home agent. If the MDfield has a value of 3, the message was sent from one foreign agent toanother foreign agent. Of course it should be understood that the abovevalues are arbitrary and any of above values may be switched withanother value.

The “A” bit indicates whether the recipient of the recovery message mustacknowledge the recovery message according to one embodiment of theinvention. For example, if the “A” bit is set to 1, an acknowledgementis required. If the “A” bit is set to 0, the acknowledgement isoptional. It should be understood that while acknowledgement messagesincrease reliability, they also increase the amount of bandwidth that isused.

According to one embodiment of the invention, the “R”, “V”, and “C” bitsindicate a particular action that the recipient should perform uponreceiving the recovery message. For example, the “R” bit indicateswhether Mobile IP session information (e.g., Mobile IP records from aMobile IP structure) is to be recovered (e.g., whether a Mobile IP needsto be reacquired). For example, if the “R” bit is set to 1, Mobile IPinformation needs to be recovered. If the “R” bit is set to 0, Mobile IPinformation does not need to be recovered. The recover action isdiscussed in greater detail with reference to FIGS. 2, 3, and 9. The “V”bit indicates whether Mobile IP session information is to be verified.For example, if the “V” bit is set to 1 Mobile IP session informationneeds to be verified. If the “V” bit is set to 0 Mobile IP sessioninformation does not need to be verified. The verification action isdiscussed in greater detail with reference to FIGS. 3, 6, and 9. The “C”bit indicates whether Mobile IP information is to be cleared. Forexample, if the “C” bit is set to 1 Mobile IP information needs to becleared. If the “C” bit is set to 0 Mobile IP information does not needto be cleared. Clearing Mobile IP information is discussed in greaterdetail with reference to FIGS. 3, 4, and 5.

The Reserved field is sent with a value of 0 and is ignored whenreceived. The Sender Address field includes the address of the sender(e.g., the IP address of the sender). The Receiver Address fieldincludes the address of the receiver (e.g., the IP address of themobility agent peer receiving this message). The Identification field isa 64 bit number constructed by the sending mobility agent used formatching recovery messages with a RECOVERY response and for protectingagainst replay attacks of notification messages. A portion of theIdentification field may also be used as a sequence number.

The extensions field may extend the functionality of the recoverymessage format. One or more extensions may be used with this recoverymessage as well as one or more authentication extensions as defined inRFC 3344. For example, according to one embodiment of the invention thefollowing extensions may be included in the extensions field of arecovery message format: capability negotiation extensions, bulk sessionrecovery request extensions, single session recovery request extensions,bulk session recovery reply extensions, and single session recoveryreply extensions.

According to one embodiment of the invention a mobility agent maynegotiate one or more capabilities with another mobility agent. Acapability represents a particular set of one or more operationsproviding functionality of an application feature. If each mobilityagent supports that capability the mobility agents may send messagesrelative to that capability (i.e., the mobility agents may make use ofthat capability). For example, mobility agents may negotiate a helloprotocol capability, which when negotiated allows the hello applicationfeature to be used. For example, a negotiated hello capability allows ahello packet to be sent between mobility agents in a recovery messageformat. Further examples of capabilities that mobility agents maynegotiate includes: Mobile IP session recover capability, Mobile IPsession verify capability, and/or Mobile IP session clear capability. Itshould be understood that the above examples are exemplary as there maybe many other capabilities that may be negotiated. Furthermore,additional information may be transmitted through recovery messages(e.g., QoS parameters, security attributes (e.g., AAA parameters), loadbalancing capabilities, rate policies, etc.).

According to one embodiment of the invention, the capability negotiationextension takes the following format:

The Type field indicates the type of extension, which in this caseindicates that this is a capability negotiation extension. The Lengthfield is the total length of the extension. The OPT field indicateswhether any options are present in the extension. The CapabilitiesSupported field indicates which capabilities the transmitting mobilityagent (i.e., the mobility agent sending the capability negotiationextension) supports. Thus, with this information the receiving mobilityagent may compare those capabilities with the capabilities that itsupports. For example, the value 0x001 in the Capabilities Supportedfield indicates that the hello protocol capability is supported. Thevalue 0x002 indicates that different recovery modes are supported; thevalue 0x004 indicates that different recovery types are supported, andthe value 0x008 indicates that different recovery actions are supported.It should be understood that additional values are contemplated by theinvention depending on different capabilities supported by the mobilityagents.

The Hello Interval field is an amount of time until sending the nexthello packet. The Dead Interval field is a multiple of the HelloInterval within which the receiving mobility agent (e.g., the peermobility agent) has to send the hello packet back to the transmittingmobility agent before being declared as dead. The Recovery Modes fieldindicates whether a periodic recovery capability is supported and/or anevent based recovery capability is supported. For example, in theperiodic mode, a recovery message is sent at some predetermined timeinterval (e.g., once a day, once an hour, etc.). In contrast, in theevent based mode, a recovery message is sent as a result of a dynamicevent (e.g., mobility agent restart, Mobile IP session conflict,administrative events (e.g., network administrator removing mobilitybindings), irrecoverable events, a hello packet with a sequence numberless than 255, etc.).

The Recovery Types field indicates whether a bulk session recovery issupported (e.g., recovering more than one Mobile IP session in a singlerecovery message) and/or whether a single session recovery is supportedaccording to one embodiment of the invention. For example, upon amobility agent restarting, that mobility agent will likely want to senda recovery message regarding every Mobile IP session (e.g., each MobileIP record) that existed on the mobility agent before the restartoccurred; thus a bulk session recovery type is appropriate. On the otherhand, if a mobile node has moved from one foreign agent to anotherforeign agent, the home agent may direct the old foreign agent to clearits Mobile IP session information regarding that mobile node; thus onlythat particular Mobile IP session is affected, in which case a singlesession recovery type may be appropriate. According to one embodiment ofthe invention, a reliable channel (e.g., TCP, STCP, etc.) may be used tocarry bulk Mobile IP session information. According to one embodiment ofthe invention, support for using the reliable channel is negotiatedduring capabilities negotiation.

The Recovery Actions field indicates the type of action that issupported by the mobility agent. For example, the Recovery Action fieldmay indicate that Mobile IP session verify, Mobile IP session recover,and/or Mobile IP session clear are supported. The Options fieldindicates whether there are options present in the extension. Processingmodules and data structures (e.g., storage of the existence andcapabilities of peers) are described later herein.

As previously described, the recovery messages are in a request/responseformat. According to one embodiment of the invention, a mobility agentmay request bulk session recovery for a specific network prefix or for anetwork access identifier (NAI) partial string (e.g., user or domain).For example, a bulk session recovery request extension for a networkprefix may have the following format:

A bulk session recovery request extension for a NAI substring may havethe following format:

According to one embodiment of the invention a mobility agent mayrequest a single session recovery. A single session recovery requestmust uniquely identify a Mobile IP session (e.g., NAI, Home Address(HoA), session creation timestamp, etc.). For example, a single sessionrecovery request extension may have the following format:

According to one embodiment of the invention a mobility agent mayrespond with a bulk session recovery response. The bulk session recoveryresponse may include information regarding multiple Mobile IP sessions.A template-based format may be used when sending the Mobile IPinformation. For example, in the case of sending Mobile IP databaserecords, each packet may have a template TLV (type, length, value) whichlists the order and type of fields that are included for each record sothat each field need not be encoded as an independent TLV. For example,a bulk session recovery reply extension may take the following format:

The “T” bit indicates whether the record is a template or a sessionrecord. The Template ID field is a unique identifier for the currentrecovery transaction. The Record SetID field is an identifier thatmatches the identifier in the template ID field. According to oneembodiment of the invention session records are deciphered based on thetemplate matching the identifier in the template ID field.

According to an embodiment of the invention a mobility agent may respondto a recovery message with a single session recovery response message. Asingle session recovery response must uniquely identify a Mobile IPsession (e.g., NAI, Home Address (HoA), session creation timestamp,etc.). For example, a single session recovery response extension mayhave the following format:

It should be understood that the above extensions (e.g., capabilitynegotiation extensions, bulk session recovery request extensions, singlesession recovery request extensions, bulk session recovery responseextensions, and single session recovery response extensions) may beincluded as part of the registration of a mobile node. For example, thecapabilities negotiation extension may be included in the usual MobileIP registration request/reply messages as defined in RFC 3344 and/orMobile IP registration revocation messages as defined in RFC 3543. Itshould be understood that the above message formats are exemplary andothers are within the scope of the invention.

FIG. 2 is a data flow diagram illustrating Mobile IP session recovery ofa foreign agent according to one embodiment of the invention. Theoperations of FIG. 2 will be described with reference to the exemplaryembodiment of FIGS. 8 and 9. However, it should be understood that theoperations of FIG. 2 can be performed by embodiments of the inventionother than those discussed with reference to FIGS. 8 and 9, and theembodiments discussed with reference to FIGS. 8 and 9 can performoperations different than those discussed with reference to FIG. 2.

FIG. 8 illustrates an exemplary mobility agent configured to supportMobile IP session recovery according to one embodiment of the invention.The mobility agent 801 represents foreign agents and home agents (i.e.,the mobility agent 801 may be a foreign agent or a home agent).Additionally, the mobility agent 801 may be one of a multiple ofinstances of mobility agents within a single network element. Referringback to FIG. 1, the foreign agents 120 and 130, and the home agents 140and 150 are each represented by the mobility agent 801. The mobilityagent 801 includes the packet processing module 810, the security module820, the mobility agent to mobility agent capabilities negotiationmodule 830, the mobility agent to mobility agent capabilities modules840, the Mobile IP data structure 850 (which includes a local mobilityagent Mobile IP structure 852 and remote mobility agent(s) Mobile IPstructure 854), a remote mobility agent configuration structure 860(which includes supported remote mobility agent(s) capabilities 862 andremote mobility agent(s) type 864), and static remote mobility agentstructure 870.

The packet processing module 810 is responsible for processing packetsreceived and sent by the mobility agent 801. The security module 820 isused during authentication of messages and of the mobile nodes (e.g.,through use of AAA). The mobility agent to mobility agent capabilitiesmodule(s) 840 provides functionality for the recovery capabilities themobility agent 801 supports. For example, the mobility agent to mobilityagent capabilities module(s) 840 include new message types for certainones of the capabilities. As previously described, a capabilityrepresents a particular set of one or more operations providingfunctionality of an application feature. For example, a capability mayinclude a capability to recover Mobile IP sessions without use of highavailability (which will be described in detail later herein). Typicalhigh availability schemes require that the mobility agent (e.g., aprimary mobility agent) be able to quickly switch over to a standbymobility agent upon a failure. The standby mobility agent requiresredundant storage, redundant processing modules, redundant control cardsand/or line cards, switchover support, etc. The standby mobility agentmay be remotely located from the primary mobility agent, or locatedwithin the same network element as the primary mobility agent. Thus, itshould be understood that high availability is expensive and certainmobility agents in a Mobile IP network need not support highavailability.

The mobility agent to mobility agent capabilities negotiation module 830negotiates the capabilities between mobility agents (e.g., throughcapabilities request/capabilities reply messages). The mobility agent tomobility agent capabilities negotiation module 830 includes support forthe new type of negotiation messages. For example, the previouslydescribed negotiation extension message type is supported by themobility agent to mobility agent capabilities negotiation module 830.The remote mobility agent configuration structure 860 is to storeconfiguration information about remote mobility agents (e.g., backupmobility agents and/or peered mobility agents) that are coupled to themobility agent 801. The supported remote mobility agent(s) capabilities862, coupled to the mobility agent to mobility agent capabilitiesnegotiation module 830, is a structure that identifies the capabilitiesa remote mobility agent supports. The remote mobility agent(s) type 864is a data structure that identifies the type of remote mobility agent(e.g., backup and/or peer). According to one embodiment of the inventionthe supported remote mobility agent(s) capabilities 862 and the remotemobility agent(s) type 864 are the same structure. The type andsupported capabilities of a remote mobility agent may determine theaction included in a recovery message the mobility agent 801 sends to,or receives from, that remote mobility agent.

The Mobile IP data structure 850 is to store Mobile IP information ofthe mobility agent 801 in the local mobility agent Mobile IP structure852 and Mobile IP information from remote mobility agent(s) in theremote mobility agent(s) Mobile IP structure 854. The remote mobilityagent(s) Mobile IP structure 854 may store Mobile IP information fromvarious remote mobility agents and/or other additional informationpertaining to mobile nodes associated with the remote mobility agents(e.g., a QoS information for that mobile node, traffic filters for thatmobile node, access control lists of that mobile node, etc.). In thecase of the mobility agent 801 being a foreign agent, the local mobilityagent Mobile IP structure 852 may be a visitor structure. In the case ofthe mobility agent 801 being a home agent, the local mobility agentMobile IP structure 852 may be a binding structure. According to oneembodiment of the invention the local mobility agent Mobile IP structure852 and the remote mobility agent(s) Mobile IP structure 854 are thesame structure.

In FIG. 2, the mobile node 110 is coupled with the foreign agent 120,and the foreign agent 120 is coupled with the home agent 140. Thus, themobile node 110 is anchored at the home agent 140 and is within theforeign network of the foreign agent 120. The foreign agent 120 and thehome agent 140 are mobility agent peers. At operation 210, the homeagent 140 and the foreign agent 120 negotiate capabilities. For example,referring to FIG. 8, the mobility agent to mobility agent capabilitiesnegotiation module 830 on the foreign agent 120 and the home agent 140is used to negotiate capabilities. If the foreign agent 120 and the homeagent 140 each support the Mobile IP session recover capability, each ofthe mobility agents include a recovery capability module as one of themobility agent to mobility agent capabilities modules 840 according toone embodiment of the invention. Additionally, the supported remotemobility agent(s) capabilities 862 of the foreign agent 120 and the homeagent 140 store information indicating whether the home agent 140 andthe foreign agent 120 support recover Mobile IP capability respectively.Additionally, the remote mobility agent(s) type structure 864 of theforeign agent 120 and the home agent 140 stores information regardingthe type of mobility agent the home agent 140 and the foreign agent 120are respectively. For example, the remote mobility agent(s) typestructure 864 of the foreign agent 120 indicates that the home agent 140is a mobility agent peer.

According to one embodiment of the invention, if a mobility agentsupports Mobile IP session recover capability, the mobility agent iscapable of storing, in the remote mobility agent(s) Mobile IP structure854, Mobile IP information and/or additional mobile node informationassociated with remote mobility agents. In addition, if a mobility agentsupports Mobile IP session recover capability, the mobility agent iscapable of transmitting local Mobile IP information and/or additionallocal mobile node information.

According to one embodiment of the invention, the Mobile IP sessionrecover capability is negotiated by piggybacking on the usualregistration request and registration reply messages as defined in RFC3344. In other words, the Mobile IP session recover capability isincluded in the extensions field of the usual registration request/replymessages. For example, upon the first registration request the foreignagent 120 forwards to the home agent, on behalf of a requesting mobilenode, the usual registration request to the home agent 140 andpiggybacks the Mobile IP session recover capability with thatregistration request. Similarly, the home agent 140, when transmitting aregistration reply, may piggyback the recover Mobile IP capability withthe registration reply message. According to another embodiment of theinvention, the Mobile IP session recover capability is negotiated by arecovery message as described previously.

Referring back to FIG. 2, after the Mobile IP session recover capabilityhas been negotiated, some time later at operation 212 the foreign agent120 receives a usual registration request from the mobile node 110. Inaddition to processing the registration request as usual (e.g., thepacket processing module 810 authenticating the mobile node with use ofthe security module 820 and making a record for the mobile node in thelocal mobility agent Mobile IP structure 852), the foreign agent 120forwards the registration request to the home agent 140 and piggybacksrecovery data in the format of foreign agent specific information atoperation 214. The foreign agent specific information is opaqueinformation (i.e., the foreign agent specific information is useful onlyfor the specific implementation of that particular foreign agent). Theforeign agent specific information includes all necessary informationrequired for restoration of one or more Mobile IP sessions. In otherwords, if the foreign agent 120 inadvertently or unexpectedly losesinformation in its local mobility agent Mobile IP structure, the foreignagent specific information includes the information to rebuild therecords in that structure. The foreign agent specific information mayinclude the access interface associated with the mobile node, anidentifier of the mobile node (e.g., MAC address, NAI, IP address),layer 2 information, layer 3 information, session username, timestamps,implementation specific information, security information (e.g., AAA),etc. Additionally, the foreign agent specific information may includeadditional information pertaining to the mobile node it is providingMobile IP services for (e.g., QoS information for that mobile node,traffic filters for that mobile node, access control lists of thatmobile node, etc.). According to one embodiment of the invention theforeign agent specific information may be obtained from a pending tableon the foreign agent 120 (e.g., from the local mobility agent Mobile IPstructure 852 on the foreign agent 120). According to one embodiment ofthe invention the foreign agent specific information is encrypted in amanner such that the home agent 140 is unable to read the foreign agentspecific information.

Thus, according to one embodiment of the invention, if Mobile IP sessionrecover capability is supported at a home agent (e.g., as indicatedaccording to the supported remote mobility agent(s) capabilities 862 ofthe peered foreign agent) and the peered foreign agent, upon a mobilenode anchored at that home agent requesting Mobile IP services from thatforeign agent (e.g., through a Mobile IP registration request message),the foreign agent dynamically and automatically triggers thetransmission of foreign agent specific information associated with thatmobile node to that home agent. Subsequent Mobile IP registrationrequests from different mobile nodes that are anchored at that homeagent also trigger the transmission of foreign agent specificinformation associated with those mobile nodes to the home agent 140. Itshould also be understood that the home agent may be one of multiplehome agents that is peered with the foreign agent. A similar process foreach of the other ones of the home agents which support Mobile IPsession recover capability is performed upon a Mobile IP registrationrequest. In this fashion, the foreign agent 120 may cause the storage ofrecovery information in the form of foreign agent specific informationon each of the peered home agents for which it is currently providingforeign agent service for (assuming that the peered home agents supportMobile IP session recover capability).

Dynamic distribution of recovery information is illustrated in FIG. 9.Referring to FIG. 9, the network element 910 includes a foreign agent920 and a home agent 930. The foreign agent 920 is peered with the homeagents 940A-940D as indicated by the communication links 944A-944D. Thecommunication link 944D is illustrated with a dashed line to indicatethat although the home agent 940D is a peer of the foreign agent 920,the foreign agent 920 is not currently providing mobile services to anymobile node anchored at the home agent 940D. The foreign agent 920 isproviding Mobile IP services to mobile node (NAI1) 911 anchored at thehome agent 940A, the mobile node (NAI2) 912 anchored at the home agent940B, and the mobile node (NAI3) anchored at the home agent 940C. Theforeign agent 920 includes a Mobile IP data structure 922 that includesforeign agent information associated with the mobile nodes 911-913, andhome agent specific information associated with the mobile node (NAI1)911 from the home agent 940A.

The home agents 940A and 940B and the foreign agent 920 each supportMobile IP session recover capability (e.g., the home agents 940A and940B negotiate Mobile IP session recover capability with the foreignagent 920 as described previously). According to one embodiment of theinvention, even though a mobility agent supports Mobile IP sessionrecover capability, that mobility agent may choose not to avail itselfof that capability for its sessions. For example, in FIG. 9, the homeagent 940B stores received mobility agent specific information fromforeign agent 920 but does not transmit any session informationpertaining to home agent 940B. A mobility agent may not desire or needto transmit mobility agent specific information to its peers (e.g., themobility agent may employ a high availability recovery scheme), butstill may choose to store remote mobility agent specific information.

According to one embodiment of the invention, when a mobile noderequests Mobile IP services from a foreign agent (e.g., through a MobileIP registration request message), the foreign agent appends the foreignagent specific information corresponding to that mobile node to theregistration request and forwards it to the home agent serving as theanchor point for that mobile node. Thus, when the mobile node (NAI1) 911requests Mobile IP services from the foreign agent 920, the foreignagent 920 appends the foreign agent specific information correspondingto mobile node (NAI1) 911 to the registration request and forwards it tothe home agent 940A, which serves as the anchor point for the mobilenode (NAI1) 911. Similarly, upon the mobile node (NAI1) 912 requestingMobile IP services from the foreign agent 920, the foreign agent 920transmits foreign agent specific information corresponding to the mobilenode (NAI1) 912 to the home agent 940B. Each transmitted foreign agentspecific information includes the data necessary for the foreign agent920 to rebuild the session associated with the respective mobile nodeupon the foreign agent 920 losing the information associated with thatsession.

The home agents 940A and 940B each store the foreign agent specificinformation they have received in the Mobile IP data structure 942A andMobile IP data structure 942B respectively. The Mobile IP data structurerecord 945A and 945B includes home agent specific information in theform of home agent data and foreign agent data respectively. The homeagent data and the foreign agent data are associated with a particularmobile node (exemplary indicated by the mobile node's NAI). While thehome agent data and the foreign agent data are shown to be associated asthe same record (e.g., record 945A and 945B), the home agent data andthe foreign agent data may be stored separately while maintaining anassociation to the respective mobile node.

The home agent 940C does not support Mobile IP session recovercapability. Accordingly, the Mobile IP data structure 942C does notinclude foreign agent specific information associated with the mobilenode (NAI3) 913. Thus, the record 945C does not include foreign agentdata.

Referring back to FIG. 2, the home agent 140, in addition to processingthe usual registration request (e.g., the packet processing module 810authenticating the mobile node with use of the security module 820 andmaking a record for the mobile node 110 in the local mobility agentMobile IP structure 852), stores the foreign agent specific informationin its Mobile IP data structure 850 at operation 216. According to oneembodiment of the invention the foreign agent specific information isstored in the remote mobility agent(s) Mobile IP structure 854 and isassociated with the record for the mobile node 110. According to anotherembodiment of the invention, the foreign agent specific information isstored along with the record in the local mobility agent Mobile IPstructure 852. Thus, the Mobile IP data structure 850 stores localmobility agent MIP information (e.g., home agent mobility bindings forthe mobile node 110) and the received foreign agent specific informationassociated with the mobile node 110. According to another embodiment ofthe invention, the foreign agent specific information is stored in aseparate structure and is associated with the record for the mobile node110.

The home agent 140 transmits the usual registration reply message andpiggybacks home agent 140 specific information to the foreign agent 120at operation 218. The home agent 140 specific information is associatedwith the mobile node 110 (e.g., the home agent 140 specific informationis derived from a record for the mobile node 110 in the local mobilityagent Mobile IP structure 852). Similarly to the foreign agent specificinformation described previously, the home agent 140 specificinformation is opaque information (i.e., the home agent 140 specificinformation is useful only for the specific implementation of the homeagent 140) and includes information necessary to rebuild the sessionassociated with the mobile node 110 in the Mobile IP structure 852. Thehome agent 140 specific information may include the access circuitassociated with the mobile node 110, an identifier of the mobile node110 (e.g., MAC address, NAI, IP address), layer 2 information, layer 3information, session username, timestamps, implementation specificinformation, security information (e.g., AAA), etc. Additionally, thehome agent 140 specific information may include additional informationpertaining to the mobile node 110 (e.g., QoS information, trafficfilters, access control lists, etc.). According to one embodiment of theinvention the home agent 140 specific information may be encrypted in amanner such that the foreign agent 120 is unable to read the home agent140 specific information.

Referring to FIG. 9, the home agent 940A has transmitted home agent 940Aspecific information associated with the mobile node (NAI1) 911 to theforeign agent 920, and the foreign agent 920 has stored that informationin the Mobile IP data structure 922.

The foreign agent 120, in addition to processing the registration replyas usual, stores the home agent 140 specific information in its MobileIP data structure 850 at operation 220. According to one embodiment ofthe invention the home agent 140 specific information is stored in theremote mobility agent(s) Mobile IP structure 854 and is associated withthe record for the mobile node 110. According to another embodiment ofthe invention, the foreign agent specific information is stored alongwith the record in the local mobility agent Mobile IP structure 852.Thus, the Mobile IP data structure 850 stores local mobility agent MIPinformation (e.g., mobile node 110 visitor information) and the receivedhome agent 140 specific information associated with the mobile node 110.According to another embodiment of the invention, the home agent 140specific information is stored in a separate structure and is associatedwith the record for the mobile node 110.

The foreign agent 120 transmits a registration reply as usual to themobile node 110 thus completing the mobile node registration process atan operation 222. According to one embodiment of the invention, mobilityagent specific extensions are removed prior to transmitting theregistration reply message to the mobile node 110.

Sometime later, at an operation 224, the foreign agent 120 has suffereda failure and/or error which causes information stored in its localmobility agent Mobile IP data structure 852 to be lost (e.g., due to arestart, administrative error (e.g., an administrator has cleared theMobile IP data structure), system error, etc.). According to oneembodiment of the invention the foreign agent 120 does not employ highavailability; thus upon the failure or error the foreign agent 120 haslost the information stored in its Mobile IP data structure 850 andcannot recover the information through high availability. However, thehome agent 140 has stored the foreign agent specific information andthis information may be used to reconstruct the Mobile IP data structureas will be described in greater detail later herein.

At an operation 226, the foreign agent 120 and the home agent 140negotiates Mobile IP session recover capability a subsequent time. Whilenot shown in FIG. 2, prior to the foreign agent 120 renegotiating MobileIP session recover capability, the foreign agent 120 determines that thehome agent 140 is a mobility agent peer. According to one embodiment ofthe invention, the list of static peers (e.g., mobility agents that havebeen manually and/or statically configured as peers of the foreign agent120) is included in a static remote mobility agent structure on theforeign agent 120. For example, referring to FIG. 8, the static remotemobility agent structure 870 stores the static peer information.According to one embodiment of the invention, the static remote mobilityagent structure 870 is not affected by the failure and/or error thatcaused the loss of information in the local mobility agent Mobile IPdata structure 852. Thus, the foreign agent 120 may determine that thehome agent 140 is a mobility agent peer with use of the static remotemobility agent structure 870.

If the home agent 140 is not indicated in the static remote mobilityagent structure 870, then the home agent 140 may be a dynamic mobilityagent peer. A dynamic mobility agent peer is a peer that is not manuallyand statically configured and is peered due to the request of the mobilenode. For example, the mobile node 110 (anchored at the home agent 140,which is not included in the static remote mobility agent structure 870)may move to the foreign network of foreign agent 120 and request MobileIP services. Upon successfully providing Mobile IP services to themobile node, the foreign agent 120 and the home agent 140 are peered.Typically, if the failure and/or error causes the foreign agent 120 torestart, the foreign agent 120 loses knowledge of the dynamic mobilityagent peers. According to one embodiment of the invention, determiningdynamic mobility agent peers may be performed through use of the helloprotocol, which is described in greater detail later herein. Accordingto one embodiment of the invention the list of the dynamic mobilityagent peers may be obtained from a remote database (e.g., AAA(authentication, authorization, accounting) server, policy server,etc.).

The Mobile IP session recover capability is negotiated after the failureor error as the foreign agent 120 may have different capabilities afterthe failure and/or error. For example, the foreign agent 120 prior tothe failure and/or error may be running a version of software (e.g.,2.0) that includes the Mobile IP session recover capability but afterthe failure and/or error the foreign agent was required to restart withan older version of software (e.g., 1.0) that does not include theMobile IP session recover capability. If the capability does not exist,then the recovery is handled as in the prior art. Thus, in oneembodiment of the invention, the mobility agents do not assume thatprevious capabilities exist after a failure and/or error. According toanother embodiment of the invention, the Mobile IP session recovercapability is not negotiated after the failure and/or error if thefailure and/or error did not cause a restart of the foreign agent 120.

Assuming that the foreign agent 120 and the home agent 140 support theMobile IP session recover capability, the foreign agent 120 transmits aMobile IP session recover request message to the home agent 140 atoperation 228. The Mobile IP session recover request message requestsinformation from the home agent 140 that will enable the foreign agent120 to reconstruct its Mobile IP data structure (i.e., requests thestored foreign agent 120 specific information). The Mobile IP sessionrecover request message may take the form as the previously describedrecovery message with one or more Mobile IP session recover requestextensions (e.g., bulk Mobile IP session request extension, singleMobile IP session request extension for each session to be recovered).As the foreign agent 120 has suffered a failure and/or error and lostits Mobile IP session information, the foreign agent 120 likely sends abulk Mobile IP session request extension if that capability is supportedon the home agent 140.

Although not shown in FIG. 2, as previously discussed the foreign agent120 may be peered with multiple home agents. If the foreign agent 120lost all of its Mobile IP session information or a portion of thatinformation, and cannot determine which of the home agents it has lostinformation about, the foreign agent 120 transmits a Mobile IP sessionrecover request message to each of the peered home agents that supportMobile IP session recover capability. The foreign agent 120 may sendMobile IP session recover requests to the peers identified in the staticpeer structure 870 that support Mobile IP session recover capability(e.g., as identified in the supported remote mobility agent(s)capabilities 862), or to dynamic mobility agent peers identified throughother means (e.g., through the hello protocol). For example, referringto FIG. 9, the foreign agent 920 sends a Mobile IP session recoverrequest to home agent 940A and to home agent 940B respectively.

The home agent 140 processes the Mobile IP session recover requestmessage and transmits a Mobile IP session recover reply message thatincludes the stored foreign agent specific information at operation 230.The Mobile IP session recover reply message may take the form as thepreviously described recovery message with a Mobile IP session recoverextension (e.g., bulk Mobile IP session recover extension, single MobileIP session recover extension). Thus, the home agent 140 transmits to theforeign agent 120 the necessary information for the foreign agent 120 toreconstruct its local mobility agent Mobile IP structure 852. Theforeign agent 120 transmits to the home agent 140 an acknowledgementthat it has received the recovery reply message at operation 232. Theacknowledgement increases the reliability that the foreign agent 120 hasreceived all of the stored foreign agent information. For example, ifthe home agent 140 does not receive an acknowledgement the home agent140 may retransmit the Mobile IP session recover reply message.According to one embodiment of the invention, the number of times theMobile IP session recover reply message is retransmitted is negotiatedduring the capabilities negotiation.

Referring to FIG. 9, the foreign agent 920 may receive the storedforeign agent information in the records 945A-945B of the home agents940A-940B respectively. Note, that as the home agent 940C does notsupport Mobile IP session recover capability and does not store foreignagent 920 specific information, the foreign agent 920 does not receiveforeign agent information from the home agent 940C.

Referring back to FIG. 2, the information received from the home agent140 is used by the foreign agent 120 to reconstruct its local mobilityagent Mobile IP structure 852 at operation 234. Thus, without using highavailability (as previously described, some mobility agents may notemploy high availability or want to utilize high availability due to itsresource costs), the foreign agent 120 is able to recover its localmobility agent structure 852 with the information received from the homeagent 140 (e.g., foreign agent 120 specific information associated withthe mobile node 110) after a failure and/or error which caused theinformation in the structure to be lost. Referring to FIG. 9, theforeign agent 920 specific information received from the home agents940A-940B may be used to reconstruct the Mobile IP data structure 922.Note that the Mobile IP information associated with the mobile node(NAI3) 913 cannot be recovered through use of the Mobile IP sessionrecover capability. Thus, the information associated with the mobilenode (NAI3) 913 may be recovered as is handled in the prior art, or asdiscussed with reference to FIG. 4.

Recovering Mobile IP information as described with regards to FIGS. 2,8, and 9 allows for a more efficient use of resources than recovery viahigh availability. For example, as previously described, a separatestandby mobility agent may be deployed in the Mobile IP network toprovide high availability. However, recovering Mobile IP information asdescribed with regards to FIGS. 2, 8, and 9 does not require a separatemobility agent nor a redundant storage, redundant processing, redundantline cards, etc. In addition, distributing mobile IP information tomultiple nodes rather than a single node is a more efficient use ofresources. In addition, distributing the recovery information tomultiple locations diversifies the recovery information thereby reducingthe risk of not being able to recover any of the information. Forexample, if all of the recovery information is stored in one location,and the recovery fails, then no information will be recovered. However,if the recovery information is stored in multiple locations and recoveryfails in some of those locations, but is successful in at least some ofthe others, at least some of the information may be recovered.

Furthermore, a mobility agent is more inclined to store Mobile IPinformation of a remote mobility agent if that information is associatedwith a mobile node the mobility agent is providing Mobile IP service to(e.g., a customer of the mobility agent). For example, the home agent940A may belong to service provider A, the home agent 940B may belong toservice provider B, and the foreign agent 920 may belong to serviceprovider C. Even though the home agent 940A and the foreign agent 920may belong to different service providers, the home agent 940A may allowfor storage of foreign agent 920 specific information associated withthe mobile node (NAI) 911 (and vice versa) to allow for faster recoveryfor its customer (e.g., the mobile node 911) in case of an error. Inother words, as the home agent 940A and the foreign agent 920 cooperateto provide Mobile IP services to the mobile node (NAI1) 911, the homeagent 940A and the foreign agent 920 also may cooperate to providerecovery for the mobile node (NAI1) 911. However, as this capabilitycosts resources of the home agent 940A (e.g., memory, processing,bandwidth, etc.) the home agent 940A may not allow storage of foreignagent 920 specific information associated with unrelated mobile nodes(e.g., the mobile node (NAI2) 912 anchored at the home agent 940B). Inother words, as the home agent 940A is not associated with the mobilenode (NAI2) 912 and does not belong to the same service provider as homeagent 940B, the home agent 940A does not want to utilize its resourcesto provide recovery for another service provider's customer (e.g.,mobile node (NAI2).

Additionally, while a notification message as described in IETF draft“draft-ietf-mip4-generic-notification-message-02.txt” may notify amobility agent peer of something during a mobile session, thenotification message cannot recover Mobile IP sessions, as thenotification message is tied to an existing mobile session. In otherwords, the notification message is only useful for currently establishedsessions and cannot be used to recover sessions. Thus, upon a failureand/or error which causes Mobile IP information (including existence ofmobile sessions) to be lost, the notification message cannot be used torecover Mobile IP sessions.

While not shown in FIG. 2, due to the failure or error of the foreignagent 120 the home agent 140 specific information stored in its localmobility agent Mobile IP structure 852 is also likely lost. Thus, inorder for the foreign agent 120 to provide recovery capability for thehome agent 140 (i.e., store the home agent 140 specific information),the home agent 140 is required to re-transmit the home agent 140specific information to the foreign agent 120. Similarly in FIG. 9, thehome agent 940A re-transmits the home agent 940A specific information tothe foreign agent 920.

It should be understood, that although the operations performed in FIG.2 are related to the foreign agent 120 recovering its local mobilityagent Mobile IP structure 852, the operations may similarly be performedupon the home agent 140 recovering sessions. Thus, In FIG. 9, the homeagent 930 is peered with the foreign agents 950A-950D over communicationlink 954A-954D respectively. The communication link 954D is a dashedline to indicate that although the foreign agent 950D is a peer of thehome agent 930, the foreign agent 950D is not currently providing MobileIP service to any mobile nodes anchored at the home agent 930. Theforeign agents 950A-950C are providing Mobile IP service to the mobilenodes 914-916 respectively. Each of the mobile nodes 914-916 areanchored at the home agent 930. The foreign agents 950A-950B and thehome agent 930 each support Mobile IP session recover capability. Theforeign agent 950C does not support Mobile IP session recovercapability. The home agent 930 includes Mobile IP data structure 932,which includes records for the mobile nodes 914-916 respectively(identified by the NAI of the mobile node). For the mobile node (NAI4)914, the Mobile IP data structure 932 stores home agent 930 specificinformation and foreign agent 950A specific information. For the mobilenode (NAI5) 915, the Mobile IP data structure 932 stores home agent 930specific information and foreign agent 950B specific information. Forthe mobile node (NAI6) 916, the Mobile IP data structure 932 stores homeagent 930 specific information. The foreign agent 950A stores in itsMobile IP data structure 952A foreign agent 950A specific informationand received home agent 930 specific information as indicated by record955A. The foreign agent 950B stores in its Mobile IP data structure 952Bforeign agent 950B specific information and received home agent 930specific information as indicated by record 955B. The foreign agent 950Cstores in its Mobile IP data structure 952C foreign agent 950C specificinformation as indicated by record 955C.

FIG. 3 is a data flow diagram illustrating Mobile IP session recoverywhere a mobile node is moving from one foreign agent to another foreignagent according to one embodiment of the invention. In FIG. 3, the homeagent 140 is coupled with the foreign agent 120 and the foreign agent130. The foreign agent 120 and the foreign agent 130 are both peers ofthe home agent 140 (e.g., the foreign agent 120 and the foreign agent134 each provides care-of-addresses for certain mobile nodes belongingto the home agent 140). At operation 300, the mobile node 110 (NAI=1) isassociated with the foreign agent 120 at a time 1. At operation 302, themobile node 110 (NAI=1) is associated with the foreign agent 120 at atime 2 (where time 2>time 1). Thus, the mobile node 110 has moved fromthe foreign agent 120 to the foreign agent 130. At an operation 304, thehome agent 140 has suffered a failure and/or an error which has causedloss of information in its local mobility agent Mobile IP structure 852.Additionally, the home agent 140 was not able to notify the foreignagent 120 to stop providing Mobile IP service to the mobile node 110prior to suffering the failure or error (e.g., through a registrationrevocation message). In addition, the lifespan associated with theMobile IP information of the mobile node 110 has not expired on theforeign agent 120. Therefore, the foreign agent 120 continues to storeMobile IP information regarding the mobile node 110 (e.g., a binding forthe mobile node 110).

As the foreign agent 120 and the foreign agent 130 are both peers of thehome agent 140 (determining that the foreign agents 120 and 130 arepeers is performed similarly as described previously herein), the homeagent 140 negotiates capabilities with the foreign agent 130 atoperation 310 and negotiates capabilities with the foreign agent 120 atoperation 312. According to one embodiment of the invention, the homeagent 140 recovers the information in the local Mobile IP structure 852through means known in the prior art (e.g., through high availability).However, the home agent 140 would like to verify that the information inthe recovered Mobile IP structure 852 is accurate. Thus, thecapabilities negotiated may include Mobile IP session verify capability.If, however, the home agent 140 does not employ recovery methods knownin the prior art (e.g., high availability), the capabilities negotiatedinclude Mobile IP session recover capability. Additionally, thecapabilities negotiated include Mobile IP session clear capability whichis described in more detail later herein.

Once the capabilities are negotiated, the home agent 140 transmits arecovery request message where the action included in the messagedepends on whether the home agent 140 is verifying one or more sessionsor recovering one or more sessions (e.g., bulk session recovery request,single session recovery request) to the foreign agent 130 at operation314, and transmits a recovery request message (e.g., bulk sessionrecovery request, single session recovery request) to the foreign agent120 at operation 316. The foreign agent 120 transmits a recoveryresponse message (e.g., bulk session recovery response, single sessionrecovery response) to the home agent 140 at operation 318. If therecovery request message in operation 316 included the Mobile IP sessionrecover action, the recovery response message in operation 318 includesforeign agent 120 specific information associated with the mobile node110. The foreign agent 120 specific information indicates that theforeign agent 120 is providing service to the mobile node 110 andincludes a timestamp (e.g., T1) of when the foreign agent 120 startedproviding service to the mobile node 110. The home agent 140 may rebuildits local mobility agent Mobile IP structure with the foreign agent 120specific information received at operation 318.

If the recovery request message in operation 316 included the Mobile IPsession verify action, the recovery response message in operation 318includes information verifying that the foreign agent 120 is providingMobile IP service to the requested mobile nodes. For example, if therecovery request is a single session recovery request for the mobilenode 110, the foreign agent 120 replies with information verifying thatthe foreign agent 120 is providing Mobile IP service to the mobile node110. If the recovery request is a bulk session recovery request, theforeign agent 120 replies with information verifying that the foreignagent 120 is providing Mobile IP services to any number of mobile nodes.In other words, the bulk session recovery request message requestsverification for each mobile node anchored to the home agent that theforeign agent is providing Mobile IP services for. Included in therecovery response message in operation 318 is information uniquelyidentifying the mobile node and a time when the foreign agent 120started providing service to the mobile node (e.g., NAI, IP address, anda timestamp). Note that this information is not opaque informationspecific to the foreign agent 120. The recovery response message inoperation 318 indicates that the foreign agent 120 is providing MobileIP services to the mobile node 110 and indicates a timestamp T1. Thehome agent 140 transmits an acknowledgement to the foreign agent 120 atoperation 320.

Similarly to the foreign agent 120, the foreign agent 130 transmits arecovery response message where the action included in the messagedepends on whether the home agent 140 is verifying one or more sessionsor recovering one or more sessions. The foreign agent 130 transmits arecovery response message (e.g., bulk session recovery response, singlesession recovery response) to the home agent 140 at operation 322. Ifthe recovery request message in operation 314 included the Mobile IPsession recover action, the recovery response in operation 322 includesforeign agent 130 specific information associated with the mobile node110. The foreign agent 130 specific information indicates that theforeign agent 130 is providing service to the mobile node 110 andincludes a timestamp (e.g, T2 (T2>T1)) of when the foreign agent 130started providing service to the mobile node 110. The home agent 140transmits an acknowledgement to the foreign agent 130 at operation 324.As the foreign agent 130 started providing service to the mobile node110 at a later time than foreign agent 120, the home agent assumes thatthe mobile node 110 has moved from the foreign agent 120 to the foreignagent 130. Thus, the home agent 140 may rebuild its local mobility agentMobile IP structure according to the foreign agent 130 specificinformation received at operation 322. For example, if the home agent140 previously rebuilt the local mobility agent Mobile IP structureaccording to the foreign agent 120 specific information received atoperation 318, the home agent 140 modifies the local mobility agentMobile IP structure with the foreign agent 130 specific information.

If the recovery request message in operation 314 included the Mobile IPsession verify action, the recovery response message in operation 322includes information verifying that the foreign agent 130 is providingMobile IP service to the requested mobile nodes in a similar fashion asdescribed regarding the recovery response message in operation 318.Included in the recovery response message in operation 322 isinformation uniquely identifying the requested mobile nodes (if theyexist) and a time when the foreign agent 130 started providing serviceto those mobile nodes (e.g., NAI, IP address, and a timestamp for eachmobile node). Note that this information is not opaque informationspecific to the foreign agent 130. The recovery response message inoperation 322 indicates that the foreign agent 130 is providing MobileIP services to the mobile node 110 and indicates a timestamp T2, whereT2 is greater than T1. The home agent 140 transmits an acknowledgementto the foreign agent 130 at operation 324.

Thus, at the time of operation 324 the home agent 140 has receivedrecovery responses from two different foreign agents regarding the samemobile node (i.e., mobile node 110 as identified by the same NAI). Aspreviously described, as the recovery response from the foreign agent130 in operation 322 indicates that the foreign agent 130 startedproviding Mobile IP services to the mobile node 110 later in time thenthe foreign agent 120, the home agent 140 assumes that the mobile node110 has moved from the foreign agent 120 to the foreign agent 130. Thus,the home agent 140 assumes that the foreign agent 120 no longer needs tostore Mobile IP information for the mobile node 110. Thus, the homeagent 140 transmits a recovery message with a Mobile IP session clearaction to the foreign agent 120 at operation 326. This recovery messagewith the clear action directs the foreign agent 120 to remove the storedMobile IP information associated with the mobile node 110. According toone embodiment of the invention, the recovery message includesauthentication information which allows the foreign agent 120 to trustthat the recovery message is from the home agent 140 and not animposter. The foreign agent 120 may then clear the Mobile IP informationassociated with the mobile node 110. For example, the foreign agent 120may clear the entry in its local mobility agent Mobile IP structure 852corresponding to the mobile node 110. Additionally the foreign agent 120may clear information that may be stored in the remote mobility agent(s)Mobile IP structure 854 corresponding to the mobile node 110. Therefore,the foreign agent 120 does not have to wait until a lifespan in theentry for the mobile node expires before removing the entry as the homeagent 140 may direct the foreign agent to remove that entry.

It should be understood that the order of operations in FIG. 3 isexemplary. For example, the home agent 140 may receive the recoveryresponse 322 from the foreign agent 130 prior to receiving the recoveryresponse 318 from the foreign agent 120. However, it should beunderstood that the home agent 140 still rebuilds its local mobilityagent Mobile IP structure according to the received foreign agent 130specific information. For example, the home agent 140 may rebuild itslocal mobility agent Mobile IP structure with the received foreign agent130 specific information at operation 322, and upon receiving therecovery response from the foreign agent 120 at operation 318, the homeagent 140 determines that the foreign agent 120 has started providingMobile IP services to the mobile node 110 at a later time than has theforeign agent 130. Thus, if the home agent 140 receives foreign agentspecific information from multiple foreign agents regarding a singlemobile node, regardless of the time the home agent 140 receives theforeign agent specific information, the home agent 140 rebuilds itslocal mobility agent Mobile IP structure according to whichever foreignagent started providing Mobile IP service to that mobile node latest intime.

FIG. 4 is a data flow diagram illustrating Mobile IP session recovery ina Mobile IP network with backup agents and/or recovery partnersaccording to one embodiment of the invention. In FIG. 4, the home agent140 is coupled with the home agent 150 and the foreign agent 120. Theforeign agent 120 is coupled with the home agent 140 and the foreignagent 130. Similarly to operation 210 in FIG. 2, the home agent 150 andthe home agent 140 negotiate capabilities at operation 402, the homeagent 140 and the foreign agent 120 negotiate capabilities at operation404, and the foreign agent 120 and the foreign agent 130 negotiatecapabilities at operation 406. According to one embodiment of theinvention the home agent 150 is a backup of the home agent 140. Forexample, the home agent 150 stores a redundant copy of informationincluded in the home agent 140 (which includes Mobile IP information).Similarly, according to one embodiment of the invention the foreignagent 130 is a backup of the foreign agent 120. For example, the foreignagent 130 stores a redundant copy of information included in the foreignagent 120.

At operation 408, the foreign agent 120 transmits a typical registrationrequest (e.g., for a particular mobile node) message to the home agent.In addition to the usual processing of the registration request, thehome agent 140 transmits a recovery message to the home agent 150indicating that the home agent 150 should add an entry for that mobilenode into its Mobile IP structure (e.g., binding structure) so as tomaintain the redundancy between the home agent 150 and the home agent140 at operation 410. At operation 412, the home agent 150 acknowledgesthe recovery message.

Once the home agent 140 receives the acknowledgement from the home agent150, the home agent 140 assumes that the home agent 150 is in aredundant state. At operation 414, the home agent 140 transmits theusual registration reply message to the foreign agent 120. In additionto the usual processing of the registration reply message (e.g., addingan entry for that mobile node its Mobile IP structure) the foreign agent120 transmits a recovery message to the foreign agent 130 indicatingthat the foreign agent 130 should add an entry for that mobile node intoits Mobile IP structure so as to maintain the redundancy between theforeign agent 120 and the foreign agent 130. At operation 418, theforeign agent 130 acknowledges the recovery message.

Sometime later, at operation 420 the foreign agent 120 transmits aregistration request with a lifetime equal to 0 (e.g., a registrationrevocation message) for a particular mobile node to the home agent 140.In addition to processing the registration request with a lifetime equalto 0 (e.g., removing the entry for that mobile node in its Mobile IPdata structure), at operation 422 the home agent 140 transmits arecovery message with a clear action to the home agent 150 directing thehome agent 150 to remove the entry for that mobile node from its MobileIP data structure so as to maintain the redundancy between the homeagent 150 and the home agent 140. The home agent 150 transmits anacknowledgement of the recovery message to the home agent 140 atoperation 424.

Once the home agent 140 receives the acknowledgement from the home agent150, the home agent 140 assumes that the home agent 150 is in aredundant state. At operation 426, the home agent 140 transmits atypical registration reply message to the foreign agent 120. In additionto processing the registration reply message (e.g., removing the entryfor that mobile node its Mobile IP structure), at operation 428 theforeign agent 120 transmits a recovery message with a clear action tothe foreign agent 130 indicating that the foreign agent 130 shouldremove the entry for that mobile node from its Mobile IP structure so asto maintain the redundancy between the foreign agent 120 and the foreignagent 130. At operation 430, the foreign agent 130 acknowledges therecovery message.

If the home agent 140 or the foreign agent 120 loses information in itsMobile IP structure, the home agent 140 or the foreign agent 120 mayrecover the information from the home agent 150 or the foreign agent 130respectively in a similar fashion as described with reference to FIG. 2.

Referring to FIG. 9, the network element 960 is coupled with the networkelement 910 and acts as a backup for the network element 910 accordingto one embodiment of the invention. The network element 960 includes astructure 962 which stores information the network element 910transmits. The structure 962 includes data from the home agent 930 andthe foreign agent 920. The structure 962 includes at least the dataspecific to the foreign agent 920 and to the home agent 930respectively. Additionally, the structure 962 may store remote mobilityagent information transmitted to the foreign agent 920 and/or home agent930. For example, the structure 962 home agent 940A specific informationstored by the foreign agent 920. If the home agent 930 and/or theforeign agent 920 loses information in its Mobile IP structure, the homeagent 930 and/or the foreign agent 920 may recover the information fromthe network element 960 in a similar fashion as described with referenceto FIG. 2.

Referring back to FIG. 4, in some embodiments of the invention the homeagent 150 is a recovery partner of the home agent 140 and similarly theforeign agent 130 is a recovery partner of the foreign agent 120. Forexample, during operation 408, the foreign agent 120 may forward theregistration request to the home agent 140 and piggyback recovery datain the format of foreign agent specific information similarly as wasdescribed in operation 214 of FIG. 2. If the home agent 140 does notwish to store the foreign agent specific information locally (e.g., thehome agent 140 does not have the internal resources available) yet wantsto provide recovery services to the foreign agent 120, it may requestits recovery partner (home agent 150) store the foreign agent specificinformation. Thus, the home agent 140 may transmit a recovery message tothe home agent 150 requesting that the home agent 150 store the foreignagent specific information at operation 410. Similarly as describedearlier, the home agent 150 acknowledges the recovery message.

At operation 414, the home agent 140 transmits the usual registrationreply message to the foreign agent 120 and piggyback recovery data inthe format of home agent specific information similarly as was describedin operation 218 of FIG. 2. Similarly as described above in reference tothe home agent recovery partner, the foreign agent 120 may request itsrecovery partner (foreign agent 130) store the home agent specificinformation. Thus, the foreign agent 120 may transmit a recovery messageto the foreign agent 130 requesting that that foreign agent 140 storethe home agent specific information at operation 416. At operation 418,the foreign agent 130 acknowledges the recovery message.

Sometime later, at operation 420 the foreign agent 120 transmits aregistration request with a lifetime equal to 0 (e.g., a registrationrevocation message) for a particular mobile node to the home agent 140.In addition to processing the registration request with a lifetime equalto 0, at operation 422 the home agent 140 transmits a recovery messagewith a clear action to the home agent 150 directing the home agent 150to remove the foreign agent specific information associated with thatsession. The home agent 150 transmits an acknowledgement of the recoverymessage to the home agent 140 at operation 424.

At operation 426, the home agent 140 transmits a typical registrationreply message to the foreign agent 120. In addition to processing theregistration reply message, at operation 428 the foreign agent 120transmits a recovery message with a clear action to the foreign agent130 directing that the foreign agent 130 remove the home agent specificinformation associated with that session. At operation 430, the foreignagent 130 acknowledges the recovery message.

FIG. 5 is a data flow diagram illustrating Mobile IP session recoverywhere a Mobile IP conflict is detected at a mobility agent according toone embodiment of the invention. In FIG. 5, the foreign agent 120 is apeer of the home agent 140. The operations 510, 512, and 514 areperformed similarly as previously described with reference to operations210, 214, and 218 as described in FIG. 2. The negotiated capabilitiesinclude at least the Mobile IP session clear capability.

During processing of the registration reply message, the foreign agent120 detects a Mobile IP session conflict at operation 516. For example,in the local mobility agent Mobile IP structure of the foreign agent120, a mobile node (e.g., MD is currently associated with the IP address1.2.3.4 (e.g., the home agent 140 has assigned the mobile node M1 to beassociated with the IP address 1.2.3.4). However, a different mobilenode (e.g., M2) is trying to register with the foreign agent 120 withthe IP address 1.2.3.4 (e.g., the home agent 140 has assigned the mobilenode M2 to be associated with the IP address 1.2.3.4). Thus the foreignagent does not know which mobile node should be associated with the IPaddress 1.2.3.4 (i.e., there is a conflict). According to one embodimentof the invention the foreign agent 120 may blindly accept the newregistration and remove the old entry or blindly reject the newregistration and keep the old entry.

According to another embodiment of the invention, the foreign agent 120transmits a recovery message with a clear action to the home agent 140upon detecting a conflict and the home agent 140 may decide which mobilenode the IP address should be associated with (i.e., the home agent 140may decide a resolution to the conflict). For example, at operation 518,the foreign agent 120 transmits a recovery message with a clear actionto the home agent 140. In one embodiment of the invention the messagedirects the home agent 140 to remove the new mobile node from its MobileIP data structure (e.g., the mobile node M2). The home agent 140 makesan independent decision whether to remove that mobile node from itsMobile IP data structure. If the home agent 140 decides to remove thatmobile node from its Mobile IP data structure, the home agent 140transmits an acknowledgement to the foreign agent 120 at operation 220.If the home agent 140 decides to keep that mobile node in its Mobile IPdata structure, the home agent 140 transmits a negative acknowledgement(e.g., nak) to the foreign agent 120 at operation 220. The foreign agent120 may then, depending on the message received from the home agent 140,remove the current mobile node from its Mobile IP data structure and addthe new mobile node to the Mobile IP data structure, or reject the newmobile node's registration.

Thus the foreign agent 120 may intelligently manage Mobile IP sessionconflicts through use of recovery messaging. Furthermore, the foreignagent 120 may notify the home agent 140 of the conflict as the homeagent 140 is likely unaware of the conflict. For example, the conflictcould have arisen due to administrative error. The network administratormay clean the bindings (e.g., clear the Mobile IP structure) on the homeagent 140 so the home agent believes that the address 1.2.3.4 is validto assign. However, when the home agent 140 assigns the address 1.2.3.4to a mobile node, it appears to the foreign agent 120 that two differentmobile nodes are assigned to the same IP address (i.e., there is aconflict). Sending a recovery message with a clear action to the homeagent allows the home agent to determine why the conflict exists and aresolution of the conflict (e.g., the home agent may direct the foreignagent as to which mobile node should be associated with that IPaddress).

Additionally, unlike a registration revocation message (as described inRFC 3543) which notifies a mobility agent peer that Mobile IP serviceshave been stopped for a particular mobile session, a Mobile IP sessionclear message may direct a mobility agent peer to update or changevalues not directly associated with the mobile session (e.g., QoSparameters, AAA parameters, load balancing attributes, rate policies,etc.). For example, a home agent may transmit a Mobile IP session clearmessage to a foreign agent to direct that foreign agent to change ratepolicies (e.g., download/upload rate) such that the rate policies areconsistent between the home agent and the foreign agent.

FIG. 6 is a data flow diagram illustrating verifying Mobile IPsession(s) according to one embodiment of the invention. In FIG. 6, theforeign agent 120 is a peer of the home agent 140. At an operation 610,the home agent has suffered a failure or error which causes informationstored in its Mobile IP data structure to be lost (e.g., due to arestart, administrative error (e.g., an administrator has cleared theMobile IP data structure), system error, etc.). The home agent 140 andthe foreign agent 120 negotiate capabilities at operation 612 in asimilar fashion as operation 210 described with reference to FIG. 2. Thenegotiated capabilities at least include Mobile IP session verifycapability. At operation 614, the home agent 140 reconstructs its MobileIP data structure (e.g., binding structure). According to one embodimentof the invention the home agent 140 reconstructs its Mobile IP datastructure through high availability.

Although the Mobile IP data structure is restored, the home agent 140does not know if the information stored in the Mobile IP data structureis accurate or current. For example, during the time that the home agent140 was inoperable due to the failure or error, a mobile node may haveleft the network, changed foreign agents, etc. Thus, at operation 616the home agent 140 transmits a recovery message with a verificationaction to the foreign agent 120. According to one embodiment of theinvention the message is a bulk recovery request message while in otherembodiments of the invention the message is a single session recoveryrequest message. The foreign agent 120 transmits an acknowledgement tothe home agent 140 for each verified Mobile IP session at operation 618according to one embodiment of the invention. According to anotherembodiment of the invention the foreign agent 120 transmits a negativeacknowledgement to the home agent 140 for each Mobile IP session that isnot verified.

While FIG. 6 illustrates a home agent verifying Mobile IP sessions witha foreign agent, it should be understood that similar operations may beperformed in regards to a home agent verifying Mobile IP sessions withanother home agent, a foreign agent verifying Mobile IP sessions with ahome agent, or a foreign agent verifying Mobile IP sessions with anotherforeign agent.

In addition, it should also be understood that verification may beperformed on multiple mobility agents distributed throughout the MobileIP network. For example, referring to FIG. 9, if the foreign agent 920and/or the home agent 930 requests Mobile IP information stored in thenetwork element 960 (e.g., after losing that Mobile IP information) theforeign agent 920 and/or home agent 930 may rebuild their respectiveMobile IP data structure and further verify the rebuilt sessions withthe mobility agent peers that support Mobile IP session verifycapability. For example, upon the foreign agent 920 receiving Mobile IPinformation from the network element 960 and rebuilding or recoveringinformation in the Mobile IP data structure 922, the foreign agent 920verifies the rebuilt sessions. For example, if the home agents 940A-940Ceach support Mobile IP session verify capability, the foreign agent 920may verify the sessions associated with the mobile nodes 911, 912, and913 with the home agents 940A, 940B, and 940C respectively (e.g.,through recovery message with a verification action and recoveryacknowledgement message similar to operations 616 and 618 in referenceto FIG. 6).

FIG. 7 is a data flow diagram illustrating a hello protocol capabilityin a Mobile IP network according to one embodiment of the invention. InFIG. 7, the foreign agent 120 is a peer of the home agent 140. Accordingto one embodiment of the invention the home agent 140 is a dynamic peerof the foreign agent 120. In other words the home agent 140 is not astatic peer of the foreign agent 120 (e.g. the home agent 140 is notincluded in the static remote mobility agent structure 870 of theforeign agent 120). Typically, when a mobility agent restarts due tosome error, the existence and identification of the static peers may berecovered; however the existence of the dynamically configured peersusually may not be recovered.

At operation 712, the foreign agent 120 and the home agent 140 negotiatecapabilities similar to operation 210 described in reference to FIG. 2.The negotiated capabilities include at least hello protocol capabilityand Mobile IP session recover capability. Once the hello protocol issuccessfully negotiated, the foreign agent 120 and the home agent 140may periodically exchange hello messages. Sometime later, at anoperation 714, the foreign agent 120 transmits foreign agent 120specific information to the home agent 140, and the home agent 140stores the foreign agent specific information in its Mobile IP structureat operation 716. At operation 718 hello messages are transmittedbetween the foreign agent 120 and the home agent 140.

According to one embodiment of the invention the hello messages enablefast detection of mobility agent failure. For example, if the foreignagent 120 stops transmitting hello messages to the home agent 140, thehome agent 140 may assume that a failure has occurred on the foreignagent 120.

Sometime later, at operation 720, the foreign agent 120 has suffered afailure and/or error which causes information stored in its Mobile IPstructure to be lost (e.g., due to a restart, administrative error(e.g., an administrator has cleared the Mobile IP data structure),system error, etc.). According to one embodiment of the invention theforeign agent 120 does not employ high availability thus upon thefailure or error the foreign agent 120 has lost the information storedin its Mobile IP data structure 850 and cannot recover the informationthrough high availability. However, the home agent 140 has stored theforeign agent specific information and this information may be used toreconstruct the Mobile IP data structure.

However, as the home agent 140 is a dynamic peer, upon the foreign agent120 failing, the foreign agent 120 likely does not have knowledge thatthe home agent 140 is a peer. Thus, the foreign agent 120 would not knowto request recovery of foreign agent specific information from the homeagent 140. However, the home agent 140 continues to send hello messagesto the foreign agent 120. At operation 722 such a hello message isreceived by the foreign agent 120. Upon receiving the hello message fromthe home agent 140, the foreign agent 120 determines that the home agent140 must be a peer (e.g., the foreign agent must have previouslynegotiated the hello protocol capability with this home agent, and theforeign agent only negotiates with its peers). At an operation 724 theforeign agent 120 and the home agent 140 negotiate capabilities assimilarly described with reference to operation 226 in FIG. 2. Thenegotiated capabilities include at least hello protocol capability andMobile IP session recover capability.

At operation 726, the foreign agent 120 transmits a hello message with asequence number less than 255. Typical hello packets have a sequencenumber over 255. Receiving a hello message with a sequence number lessthan 255 is a signal for the home agent 140 to transmit the storedforeign agent specific information to the foreign agent 120. Thus, atoperation 728, the home agent 140 transmits the stored foreign agentspecific information to the foreign agent 120 (e.g., through use of arecovery reply message). At an operation 730 the foreign agent 120transmits an acknowledgement to the home agent 140. The foreign agent120 reconstructs its Mobile IP data structure (e.g., a visitorstructure) with the received information at an operation 732.

Thus, a hello protocol capability may be negotiated between two mobilityagents. The hello protocol allows for faster detection of mobility agentfailure. The hello protocol also may be used to determine any mobilityagent peers that are dynamic peers (e.g., that are using dynamictunnels). Additionally, the hello protocol may be used to signalmobility agents (e.g., a hello message with a sequence number less than255) that recovery is requested.

In one embodiment of the invention capabilities are not negotiatedbetween mobility agents. For example, if it can be assumed that eachmobility agent supports a particular capability, then there thatcapability does not need to be negotiated. For example, if mobilityagents in the Mobile IP network are from the same vendor or operatesimilarly (e.g., support similar software) then capabilities need not benegotiated. Additionally, if the mobility agent does not receive arecovery response message after a predefined number of recovery requestmessages (e.g., three messages) then the mobility agent assumes thecapability is not supported.

In one embodiment of the invention whether capabilities are negotiatedis determined by a configuration by a network administrator. Forexample, if it can be assumed that certain capabilities are supported bymost mobility agents (e.g., commonly supported capabilities) the networkadministrator configures the mobility agent to not perform capabilitiesnegotiation for those particular capabilities. On the other hand, ifcertain capabilities may not be supported by most mobility agents (e.g.,rarely supported capabilities) the network administrator configures themobility agent to perform capabilities negotiation for those particularcapabilities.

While the flow diagrams in the figures show a particular order ofoperations performed by certain embodiments of the invention, it shouldbe understood that such order is exemplary (e.g., alternativeembodiments may perform the operations in a different order, combinecertain operations, overlap certain operations, etc.)

While the invention has been described in terms of several embodiments,those skilled in the art will recognize that the invention is notlimited to the embodiments described, can be practiced with modificationand alteration within the spirit and scope of the appended claims. Thedescription is thus to be regarded as illustrative instead of limiting.

1. A computer implemented method for recovering Mobile IP information,comprising: each of a plurality of mobility agents acting as a foreignagent for a plurality of mobile nodes communicatively coupled with thatmobility agent and creating a plurality of foreign agent type mobilitysessions for the plurality of mobile nodes; storing, within each of theplurality of mobility agents, foreign agent specific information usedonly by that mobility agent acting as foreign agent for each of itsplurality of foreign agent type mobility sessions, wherein each of theplurality of mobile nodes has another of the plurality of mobilityagents as its home agent; distributively backing up the foreign agentspecific information to the home agents by storing, for each of theplurality of foreign agent type mobility sessions, the foreign agentspecific information in the home agent of the mobile node for which thatsession was created, wherein the foreign agent specific information isnot used by the home agents; and upon one of the plurality of mobilityagents losing its foreign agent specific information about one or moreof its plurality of foreign agent type mobility sessions, recoveringthat lost foreign agent specific information from those of the pluralityof home agents it was backed up on.
 2. The computer implemented methodof claim 1, further comprising: storing, within each of the plurality ofmobility agents, home agent specific information for those of theplurality of mobile nodes it is the home agent for; distributivelybacking up the home agent specific information to the foreign agents bystoring, for each of those mobile nodes it is the home agent for, thehome agent specific information in the foreign agent of the mobile nodefor which a corresponding foreign agent type mobility session wascreated, wherein the home agent specific information is not used by theforeign agents; and upon one of the plurality of mobility agents losingits home agent specific information about one or more of its mobilenodes, recovering that lost home agent specific information from thoseof the plurality of foreign agents it was backed up on.
 3. The computerimplemented method of claim 2, wherein distributively backing up theforeign agent specific information includes piggybacking the foreignagent specific information with a Mobile IP registration requestmessage, and wherein distributively backing up the home agent specificinformation includes piggybacking the home agent specific informationwith a Mobile IP registration reply message